Passive dosing dispensers of various geometries are disclosed in prior art patents. For instance, U.S. Pat. No. 650,161 which issued to J. Williams et al. on May 22, 1900 and U.S. Pat. No. 1,175,032 which issued to E. R. Williams on Mar. 14, 1916 disclose passive dispensers which are alternately flooded and then syphoned to a predetermined level. Also, U.S. Pat. No. 3,772,715 which issued to L. V. Nigro on Nov. 20, 1973, and U.S. Pat. No. 3,781,926 which issued to J. Levey on Jan. 1, 1974, and U.S. Pat. No. 3,943,582 which issued to J. Daeninckx et al. on Mar. 16, 1976 disclose passive dispensers which are alternately flooded and then gravitationally drained. Moreover, U.S. Pat. No. 3,407,412 which issued to C. T. Spear on Oct. 29, 1968, and U.S. Pat. No. 3,444,566 which issued to C. T. Spear on May 20, 1969 disclose dispensers which, although they have no moving parts, must be connected to a pressurized water supply such as the trap refill tube in a toilet tank and in which the direction of flow alternates in labyrinth passages.
Passive dosing dispensers of the type disclosed in the commonly assigned U.S. Pat. No. 4,208,747 issued to Robert S. Dirksing on June 24, 1980 and entitled PASSIVE DOSING DISPENSER EMPLOYING TRAPPED AIR BUBBLE TO PROVIDE AIR-LOCK, which is hereby incorporated herein by reference, have solved many of the problems associated with the aforementioned prior art dispensers, most particularly the problem of providing solid product and liquid product solution isolation from surrounding toilet tank water during quiescent periods. Dispenser embodiments of the type generally disclosed in FIGS. 1 and 15-18 of the aforesaid U.S. Patent of Robert S. Dirksing, which function in a manner generally similar to the improved dispenser embodiments of the present invention, have been found particularly suitable for dispensing liquid solutions formed from solid products containing a surfactant. However, in some instances the product additive solution needs to be discharged at a relatively slow rate and it is conceivable that the toilet tank would refill with water prior to completion of the discharge operation. If the toilet tank refilled up to the inlet/discharge port of the syphon tube before the discharge operation was completed, then there would be no way to reform the air bubble and reform the air lock to provide for isolation of the product solution from the surrounding toilet tank water in a dispenser embodiment of the type disclosed in the aforesaid U.S. Patent of Robert S. Dirksing since the air bubble would have been discharged along with the product solution at the beginning of the discharge operation.
In addition, some compositions of the solid product used to form the product additive solution are somewhat slow to disperse in the toilet tank water. In such instances, it becomes preferable to provide a sufficient amount of time for the dispersion of the product solution into the toilet tank water to occur so that the additive product solution can function optimally. One method to accomplish this would be to provide a means for retarding the solution discharge, e.g., an enlarged discharge reservoir at the end of the syphon tube with an appropriately sized inlet/discharge port or ports, such that the bulk of the solution is discharged after the flush cycle is completed, i.e. when the toilet tank is refilling. This allows the solution to disperse into the toilet tank water during the quiescent periods between each flush. The dispensers of the aforesaid U.S. Patent of Robert S. Dirksing do not provide a means for such a delayed discharge.